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C#連接MySQL數據庫

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連接數據庫、執行sql語句需要的API,數據庫都有提供相關動態鏈接庫。

  幫助文檔在C:\Program Files (x86)\MySQL\Connector.NET 6.9\Documentation下的ConnectorNET.chm

1.添加動態鏈接庫文件:

  安裝數據庫MySQL時要選中Connector.NET 6.9的安裝,將C:\Program Files (x86)\MySQL\Connector.NET 6.9\Assemblies裏v4.0或v4.5中的MySql.Data.dll導入項目。v4.0和v4.5,對應Visual Studio具體項目 屬性-應用程序-目標框架 裏的.NET Framework的版本號

2.建立連接(MySqlConnection)

using MySql.Data.MySqlClient;

String connetStr = "server=127.0.0.1;port=3306;user=root;password=root; database=minecraftdb;";

// server=127.0.0.1/localhost 代表本機,端口號port默認是3306可以不寫

MySqlConnection conn = new MySqlConnection(connetStr);

try

{    

      conn.Open();//打開通道,建立連接,可能出現異常
Console.WriteLine("已經建立連接"); //在這裏使用代碼對數據庫進行增刪查改 } catch (MySqlException ex) { Console.WriteLine(ex.Message); } finally { conn.Close(); }

3.捕捉異常(MySqlException)

  連接錯誤時MySqlConnection會返回一個MySqlException,其中包括2個變量:

  Message: A message that describes the current exception.

  Number: The MySQL error number. (0: Cannot connect to server. 1045: Invalid user name and/or password.)

catch (MySqlException ex)

{

    switch (ex.Number)

    {

        case 0:

        Console.WriteLine("Cannot connect to server.  Contact administrator");

        break;

    case 1045:

        Console.WriteLine("Invalid username/password, please try again");

        break;

    }

}            

4.增刪查改的代碼(MySqlCommand、MySqlDataReader)

(1) 查詢

查詢條件固定

string sql= "select * from user";

MySqlCommand cmd = new MySqlCommand(sql,conn);

MySqlDataReader reader =cmd.ExecuteReader();//ExecuteReader()用於生成一個MySqlDataReader對象

while (reader.Read())//讀取下一頁數據,返回值是bool

{

    //Console.WriteLine(reader[0].ToString() + reader[1].ToString() + reader[2].ToString());

    //Console.WriteLine(reader.GetInt32(0)+reader.GetString(1)+reader.GetString(2));

    Console.WriteLine(reader.GetInt32("userid") + reader.GetString("username") + reader.GetString("password"));//推薦這種方式

}

需要查詢返回一個值

string sql = "select count(*) from user";

MySqlCommand cmd = new MySqlCommand(sql, conn);

Object result=cmd.ExecuteScalar();//執行查詢,並返回查詢所返回的結果集中第一行的第一列。所有其他的列和行將被忽略。select語句無記錄返回時,ExecuteScalar()返回NULL值

if (result != null)

{

    int count = int.Parse(result.ToString());

}

查詢條件不固定

//string sql = "select * from user where username=‘"+username+"‘ and password=‘"+password+"‘"; //我們自己按照查詢條件去組拼

string sql = "select * from user where username=@para1 and password=@para2";//在sql語句中定義parameter,然後再給parameter賦值

MySqlCommand cmd = new MySqlCommand(sql, conn);

cmd.Parameters.AddWithValue("para1", username);

cmd.Parameters.AddWithValue("para2", password);

 

MySqlDataReader reader = cmd.ExecuteReader();

if (reader.Read())//如果用戶名和密碼正確則能查詢到一條語句,即讀取下一行返回true

{

    return true;

}

(2) 插入、刪除、更改

string sql = "insert into user(username,password,registerdate) values(‘啊寬‘,‘123‘,‘"+DateTime.Now+"‘)";

//string sql = "delete from user where userid=‘9‘";

//string sql = "update user set username=‘啊哈‘,password=‘123‘ where userid=‘8‘";

MySqlCommand cmd = new MySqlCommand(sql,conn);

int result =cmd.ExecuteNonQuery();//3.執行插入、刪除、更改語句。執行成功返回受影響的數據的行數,返回1可做true判斷。執行失敗不返回任何數據,報錯,下面代碼都不執行

5.事務(MySqlTransaction)

String connetStr = "server=127.0.0.1;user=root;password=root;database=minecraftdb;";

MySqlConnection conn = new MySqlConnection(connetStr);

conn.Open();//必須打開通道之後才能開始事務

MySqlTransaction transaction = conn.BeginTransaction();//事務必須在try外面賦值不然catch裏的transaction會報錯:未賦值

Console.WriteLine("已經建立連接");

try

{

    string date = DateTime.Now.Year + "-" + DateTime.Now.Month + "-" + DateTime.Now.Day;

    string sql1= "insert into user(username,password,registerdate) values(‘啊寬‘,‘123‘,‘" + date + "‘)";

    MySqlCommand cmd1 = new MySqlCommand(sql1,conn);

    cmd1.ExecuteNonQuery();

 

    string sql2 = "insert into user(username,password,registerdate) values(‘啊寬‘,‘123‘,‘" + date + "‘)";

    MySqlCommand cmd2 = new MySqlCommand(sql2, conn);

    cmd2.ExecuteNonQuery();

}

catch (MySqlException ex)

{

    Console.WriteLine(ex.Message);

    transaction.Rollback();//事務ExecuteNonQuery()執行失敗報錯,username被設置unique

    conn.Close();

}

finally

{

    if (conn.State != ConnectionState.Closed)

    {

        transaction.Commit();//事務要麽回滾要麽提交,即Rollback()與Commit()只能執行一個

        conn.Close();

    }

}

總結:

MySQL動態鏈接庫提供了8個類,而上面常用操作只用到了這4個類

(1)MySqlConnection: 連接MySQL服務器數據庫。

(2)MySqlCommand:執行一條sql語句

  a.ExecuteReader——用於查詢數據庫。結果通常是MySqlDataReader對象中返回。

  b.ExecuteNonQuery——用於插入和刪除數據。

  c.ExecuteScalar——用於返回一個值。

(3)MySqlDataReader: 包含sql語句執行的結果,並提供一個方法從結果中閱讀一行

(4)MySqlTransaction: 代表一個SQL事務在一個MySQL數據庫。

(5)MySqlException: MySQL報錯時返回的Exception

還有這3個類 的相關操作未涉及, 大家可以去看幫助文檔ConnectorNET.chm在C:\Program Files (x86)\MySQL\Connector.NET 6.9\Documentation裏面

MySqlCommandBuilder: Automatically generates single-table commands used to reconcile changes made to a DataSet with the associated MySQL database.

MySqlDataAdapter: Represents a set of data commands and a database connection that are used to fill a data set and update a MySQL database.

MySqlHelper: Helper class that makes it easier to work with the provider.

C#連接MySQL數據庫